Hard product and method of making same



Patented Apr. 3, 1934 UNITED STATES PATENT OFFICE HARD PRODUCT ANDMETHOD OF MAKING SAME No Drawing. Application March 1, 1933, Serial No.659,245. In Sweden November 8, 1932 10 Claims. ,(Cl. 92--21) Theinvention relates to the manufacture of hard articles or products. e. g.boards for building and fitting purposes, or doors, tables, etc., and ismainly characterized in that cellulose or cellulosic(cellulose-containing) material which may or may not contain lignin orligneous substances is treated together with urea and/or thiourea underheat and/or pressure so as to bring the material to the desired form orthickness.

In the production of insulating board by treating wood fiber materialunder heat and pressure I have made the discovery that an addition tothe mass of carbamide (urea) or thiocarbamide (thiourca) or a mixture ofboth results in a board of superior tensile and breaking strengths, hardand glossy surface and light and attractive colour, which board also inother respects surpasses the heretofore known insulating boards producedby hot-pressing ground wood or exploded fiber material.

This surprising eifect may be due to a condensation'between the ligninin the cellulosic material and the urea and/or thiourea. Theconstitution of the lignin bodies is still comparatively unknown but tojudge from the results obtained by me it would seem that lignin willreact as an aldehyde to form condensation products with urea and/orthiourea.

Products of considerable hardness and strength may, however, be obtainedalso by hot-pressing cellulose which is substantially free from lignins,together with urea and/or thiourea although these products are not quiteof the same high quality as that obtained when lignin is present. Nodefinite theory to explain this fact can be advanced, although it may beassumed that the hydroxyl groups of the cellulose are involved in thisconnection.

As stated the primary cellulosic material together with an addition ofurea. and/or thiourea is subjected to a treatment with the applicationof heat and/or pressure. The pressure and heating steps may be quiteindependent of each other,

as it is possible, for instance, to dry the material completely orpartially prior to the pressing operation.

The method according to the invention is especially adapted for use inthe production of fiber board of the wallboard type and will bedescribed below in conn ction with such application, it being understoodhowever. that this embodiment is only an example of The many possiblevariutions of the process according to the invention.

The raw material such as wood in small pieces or chips is firstconverted into fiber. For example, it is subjected in a closed highpressure chamber to penetration by elastic fluid such as steam, underpressure, and is then progressively forced out from said chamber. Priorto the forming operation the mass may be soaked in water, if desiredcontaining sizing and fireproofing agents as well as urea and/orthiourea. The raw material may however be ground or fibrated in otherways so long as the lignins or the principal part thereof are retained.

After the fibration. a refinement as in a beater or the like is notessential and if there is any further refinement, same is preferably notextensive.

The fiber is formed into sheets from a water bath, which contains insolution carbamide CO(NH2)2 and/or thiocarbamide CS NH2)2, and in which,if desired, also materials for making the product more waterproof orfire resistant or both may be present. The quantity of carba- 'mide orthiocarbamide or a mixture of both should be proportioned so as toamount to 0.1 to 10%, preferably 5% by weight calculated on the drymaterial.

Some of the excess water may be eliminated by preliminary pressing ofthe sheet or the like as by means of squeezing rolls.

The sheets or objects thus obtained are dried under heat and pressure.If it is desired that the material be in the form of board the same ispreferably first prepared as a long sheet which is cut into lengths asdesired, and these sections are introduced into a heated press, as, forexample, between steam heated press platens.

Pressures ranging between 10 and 450 kgs/cm depending upon the nature ofthe added substances have given very satisfactory results. Thetemperature of the press platens may vary be tween 100 and 260 0.,preferably between 160 and 180 C. In most cases a pressure of aboutkgs/cm ought to be sufficient.

The heating and the pressing steps may also be effected independent ofeach other. Thus the material may be completely or partially dried priorto the beginning of the pressing operation. After the mass has beenpressed to the desired thickness the boards thus obtained are removedfrom the hot press. The product is hard and of light exterior and showsexcellent qualities of strength. It has been found that the best resultsare obtained if the pressed mass is allowed to cool while maintainingthe pressure acting thereupon, it being possible, if desired, toaccelerate the cooling eg. by the supply for instance to the pressplatens of cold mediums. as liquids, e. g. water, or gases, e. g. air.The pressure acting upon the mass may also be reduced slowly,continuously or intermittently, during the cooling of said mass.

According to another embodiment the mass is pressed between apressure-actuated platen which is adapted to be heated, and a wiregauze, for instance a wire cloth whereby the elimination of moisture isfacilitated and the drying accelerated. According to still anotherembodiment the mass, prior to the pressing, is formed into sheets whichare then enveloped by wire gauze, heat and pressure being subsequentlyapplied.

One may also first dry without special pressure and then press undercontinued drying. Also the pressing operation may obviously beinterrupted at an earlier stage, the drying then being completed withoutthe application of pressure although best results are obtained by dryingand subsequent cooling under pressure in the press.

Generally the pressing operation is effected at a temperature and apressure which are so proportioned that the added substance orsubstances are not decomposed. If comparatively elevated presstemperatures are desired such may be used if care is takenthat thedecomposition of the urea and/or thiourea is prevented at the operatingtemperature through the application of pressure, for instance so thatthe process is efiected e. g. between press platens in a closed pressurechamber which contains vapours of the urea and/or thiourea.

As stated above such embodiments are also within the spirit of theinvention where one adds substances which, while not reacting with thelignin or cellulose under ordinary conditions, yet under the operatingconditions e. g. by treatment under heat or pressure are transformed orconverted into urea and/or thiourea or will for m urea and/ or thioureawith other substances present, e. g. especially added bodies.

Thus ammonium cyanate may be used instead of urea, or one may useammonium carbamate which is converted by heating according to theequation:

NH2.CO.ONH4 CO NH) 2 +H2O The invention also comprises a product,especially fiber boards, substantially consisting oi cellulose and/orlignin in which at least part 01 the cellulose and/or lignin has formeda reaction product, possibly a condensation product with urea and/orthiourea.

What I claim is:-

1. Method of making hard products which comprises heating a mixture of acellulosic material and a urea and molding the mixture under pressure.

2. Method as defined in claim 1 in which the cellulosic materialcontains ligneous substances.

3. Method as defined in claim 1 in which the urea is carbamide.

4. Method as defined'in claim 1 in which the urea is thiocarbamide.

5. Method as defined in claim 1 in which the mixture is molded underheat and pressure.

6. Method of making hard products which comprises forming an aqueoussuspension of wood fiber containing a urea, forming a sheet therefrom,and subjecting the sheet to heat and pressure.

'7. Method as defined in claim 1 in which the urea content of themixture is from 0.1 percent to 10 percent calculated on the dry weightof the cellulosic material.

8. Method as defined in claim 1 in which the urea content of the mixtureis about 5 percent calculated on the dry weight of the cellulosicmaterial.

9. Method of making hard products which comprises intimately mixing afinely divided fibrous cellulosic material with from 0.1 percent to 10percent of its weight of a urea and heating the mixture at a temperatureof from C. to 260 C. under a pressure of from 10 to 450 kilograms persquare centimeter.

10. As a new articlev of manufacture a hard product formed by moldingunder heat and pressure a mixture of a cellulosic material and a urea.

OSSIAN WALDEMAR SANDELL.

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